50 
MORPHOLOGY OF THE CELL. 
most carefully examined consist of a mixture of two ingredients of different 
solubility; the two are so combined that when the more soluble is slowly removed, 
the less soluble remains as a skeleton (Nägeli). 
Their form varies greatly in different plants; they appear as cubes, tetrahedra, 
octohedra, rhombohedra, and in other forms ; usually, however, their crystallographic 
characters cannot be exactly defined, a consequence of their small size and of the 
inconstancy of their angles. 
In the rapidly growing organs of flowering plants they are known only in 
LathrcBa squamaria ^ ; more commonly they are produced in cells where large 
quantities of reserve-materials are collected which are only turned to use at a later 
period. The crystalloids themselves appear to be a form of protoplasmic structure 
especially adapted for a dormant condition (as in potato-tubers and many oily 
seeds) ; they are seldom found in cells which contain sap (potato-tubers), but more 
often in cells which do not contain it, and especially in oily seeds. Crystalloids 
containing colouring matters are found in petals and fruits. Sometimes they are 
formed only after the action of alcohol or a solution of sodium chloride on the 
plants externally or internally (Rhodospermin). 
The crystalloids of potato-tubers are imbedded in the protoplasm; those that 
are widely distributed in the tissues of LaihrcEa squarnaria are contained in great 
numbers in the interior of the nucleus; those found in oily seeds are generally 
enclosed in aleurone-grains. 
The crystalloids discovered by Cohn in the tubers of the potato are convenient for 
observation ; they are found very abundantly in some kinds, in others less frequently, 
in the parenchymatous cells which contain but little starch beneath the skin but 
tolerably deep in this tissue, lying enclosed in the protoplasm. Generally they are in 
the form of perfect cubes (less often of derivative forms, as tetrahedra). Those found 
by Radlkofer in the nucleus of the cells of Lathrcea squamaria lie together in great 
quantities ; they have the form of thin rectangular plates ; sometimes they have rhombic 
or trapezoid forms ; Radlkofer thinks it most probable that they belong to the rhombic 
system. In these cases they may be seen in sections without further preparation, and 
their relation to their surroundings is clear. The case is different with the crystalloids 
of oily seeds enclosed in aleurone-grains ; I shall recur to their properties, and will only 
mention that from the brazil-nut they are obtained in quantities by washing the crushed 
oily parenchyma by oil or ether, the crystalloids settling down in the form of a fine 
powder; in sections but little can be made out. They were carefully investigated in 
the isolated state by Nägeli ; according to him they appear rhombohedral, octohedral, 
or tabular; but it is uncertain whether they belong to the hexagonal or the klino- 
rhombic system. Dried and then placed in water, they alter their angles about 2° or 3°; 
in potash solution they swell strongly and alter their angles 15° or 16°. By weak acids 
and dilute glycerin a substance is extracted, and a weak skeleton with firmer skin 
remains behind. The crystalloids in the cells of the endosperm of Ricinus communis 
are, like all crystalloids, insoluble in water, and are easily seen when thin sections of the 
tissue are laid in water, which destroys the substance surrounding the crystalloid, and' 
sets it free. They frequently take the form of octohedra or tetrahedra, less often of 
rhombohedra; but the system is not certainly determined. The crystalloids which 
contain colouring matters were first detected by Nägeli in an imperfect form in the 
^ [According to Prillieux, the brown colour of Neottia nidus-avis is due to brown crystalloids 
which assume a green colour when the plant is immersed in alcohol or boiling water ; see Ann. des 
Sei. Nat., 5th ser., vol. XIX. p. 108.] 
